Fluids are injected into wells for various purposes, such as drilling and hydraulic fracturing (“fracing”). During the fracing process, a blender at the well site mixes various chemicals and proppants, such as sand, with water. The chemicals include friction reducers and viscosity enhancers. The blender feeds the mixture to high pressure pumps that inject the mixture into the well to create fractures. The pressure may exceed 10,000 psi.
With wells having long horizontal sections, it is common to perforate the casing at a lowest zone, frac the lowest zone, then install a plug. The operator then perforates a next to the lowest zone and repeats the process. It is not uncommon for an operator to perforate twenty or more zones and install twenty or more plugs in a well. Afterward, the operator lowers a drill string into the well and drills out the frangible plugs.
While drilling out the plugs, the operator circulates drilling fluid with high pressure pumps. The output pressures are typically in the 2500 to 5000 psi range and the flow rates at least 20 gpm (gallons per minute). It is important to circulate the cuttings or fragments of the plugs being drilled up with the drilling fluid. As a result, an operator typically adds friction reducers and chemicals or viscosifiers such as liquid gels to the well fluid in a blender. The friction reducers and viscosifiers are normally polymers. After the desired viscosity has been reached, the operator delivers the drilling fluid from the blender to the high pressure pumps. Blending can be time consuming, which adds to the total time to drill out the wells containing the temporary frac plugs.
Mixing devices and systems such as low, or zero, pressure surface blending systems, low pressure batch mixing systems, low pressure surface hydration systems and other such systems primarily depend on time. Conventional blenders use atmospheric tanks, internal stirring paddles, and/or some form of non-positive suction and/or displacement high pressure jetting. The blending unravels and shear stresses component molecules of the chemicals being introduced. The oil and gas industry has historically used small mobile high pressure jetting devices inside surface blending tanks as mentioned above that suck in the fluid and chemicals, and/or polymers, in a non-positive fashion as compared to total tank volume. The jetting devices ultimately jet the mix through the high pressure jet nozzles, attempting to shear stress the molecules, ultimately allowing for hydration of the entire tank mix through time. Due to the nature of this not being a positive displacement process as compared to total tank volume, and having to recirculate the fluid mix over and over in an effort to ensure that all molecules are shear stressed, this process can take up to several hours to achieve near full hydration of greater than 90%. Blending is done in efforts to bring multiple components ultimately into one homogeneous and consistent blend of quality product with enhanced chemical and physical characteristics.
As will be apparent from the previous paragraph, the prior art teaches that the various fluid types, chemicals, polymers (gels), minerals and/or gases are mixed, blended and hydrated on the low pressure side, or upstream, of the high pressure positive displacement liquid fluid pump. This low pressure mixing is normally done utilizing a variety of apparatuses and a mixture or combination of non-positive suction and/or displacement paddle mixers, mixing jets, pipes, and batch mixing tanks. A batch mixer is generally equipped with a means of adding dry and liquid chemicals, an agitation or circulation system and a manifold system to deliver the prepared fluid to storage tanks or treating pumps and/or other applications as previously described. The blended component stream is then transferred to the high pressure positive displacement liquid fluid pumps utilizing low pressure centrifugal pumps. As the homogeneous, or non-homogeneous, blend moves from its low pressure environment to and through the high pressure positive displacement liquid fluid pumps, the pumps generate the high pressures required in efforts to move the component blend fluid stream down pipes or other apparatus into and down the wellbore.